The present invention relates to apparatus for feeding a lower pressure liquid to a higher pressure system, in particular for returning condensate directly to a boiler in a steam-using system, as well as for pumping a liquid from a lower level to a higher one.
In steam-using systems, condensate is usually discharged from the system through a steam trap as soon as it is converted from steam after releasing its latent heat, however, the condensate still contains a considerable amount of heat. Conventionally, the condensate is not recycled except in occasional instances where it is utilized in a waste heat device. Accordingly, it is desirable to return the condensate directly to a boiler for recovering its entire heat content rather than discarding it, because the condensate is suitable for use in the boiler. Recently, the condensate has been returned to a boiler, usually by means of a pumping trap.
In conventional pumping traps, a float is operatively interconnected to two valves through a lever mechanism, one of the valves introduces a higher pressure medium into the trap for driving the condensate and the other valve affords an exhaust or vent from the trap. Accordingly, as the float rises and falls with the level of the condensate in the trap, it operates the valves so that while one is opened the other is closed. Further, a check valve is provided in each of an inlet passage into and an outlet passage from the trap so that the condensate can be admitted into the trap and then returned to the boiler.
In such an arrangement, it is difficult to ensure perfect coordination in the opening and closing of the valves and, since the valves are interconnected with the float through a lever mechanism, a slight shift of the float due to the upward and downward movement of the condensate level results in the commencement of one cycle operation of the trap, in such a cycle operation the amount of condensate returned is very small and cannot be predetermined and, further, a large amount of the condensate always remains in the trap. As a result this type of pumping trap cannot be used for returning large quantities of the condensate. Moreover, because of the lever mechanism, the structure of the trap is very complex and it is very difficult to maintain.